In many intracorporeal devices in the medical field, an operating head that is attached to an end of a drive shaft must be both rotated and advanced into a body in a controlled manner to perform a medical procedure. For many medical devices, control of the device's movement in the body is manifestly critical to the safety and reliability of the devices. For example, uncontrolled movements may cause damage to healthy tissue in the body. It is desirable for the drive shaft to smoothly transmit rotational torque from a drive system to the operating head. At times, the drive shaft may need to operate at high speeds, such as about 500 to 200,000 rpm's. The connection between the drive system and drive shaft must be able to accommodate these high speeds, and yet, maintain steady torque transmission.
Furthermore, some medical procedures require advancement of a lightweight rotating system to or through a treatment site, where advance motion of the rotating drive is independent of a heavy motor drive system, as well as independent in motion relative to a guidewire over which a device travels. Furthermore, some treatments require a delicate interaction and thus mandate low inertial masses of the rotating drive system, requiring a drive transmission to be small and efficient. Moreover, some medical procedures require the operator to use tactile sensitivity in holding the device to assess the operation of the device. Therefore, interferences due to rickety rotational torque may disturb the operator's tactile sense or cause other interruptions of the operation.
Intracorporeal medical devices that include drive shafts are employed for therapeutic and/or diagnostic procedures. Particular methods of using atherectomy and thrombectomy devices involve placement of a guiding catheter into the body and insertion of a guidewire, over which the operating head attached to the drive shaft is guided to a target site where an occlusion is located within a blood vessel. However, devices that do not employ guidewires are also possible. The drive shaft extends within the lumen of an operating catheter to effectively isolate the rotating elements of the device from direct contact with any healthy body matter, e.g. tissue. The catheter is fixed to the operating head at its distal end in a manner that maintains the catheter in a static position relative to the rotating drive shaft and maintains the seal of the catheter lumen. The operating head is advanced and rotated to cut or ablate the obstruction and to restore or improve blood flow in the vessel.
A general challenge of operating an intracorporeal device is that it is often difficult to guide the operating head attached to the drive shaft and/or catheter through the body to reach the area of interest, i.e. target site. The intracorporeal device must usually be routed along a tortuous path, through various internal structures within the body before arriving at the target site. For example, an obstructed blood vessel may be located in peripheral vessels, coronary vessels, cranial vessels, or other areas. The path may be of varying lengths depending on where the target site is relative to the site in the body for insertion of the intracorporeal device, i.e. insertion site. For example, the device is often inserted into a leg of a patient and then directed to the heart, head, other leg, kidney, etc. It is beneficial, then, for the intracorporeal device to allow for varying lengths of catheter and drive shaft to be inserted in the body.
During the operation, it is often necessary to move the operating head back and forth to properly operate on the target site. The intracorporeal device should provide for a means to control a smooth back and forth motion in a manner that produces little friction. Moreover, at times, unwanted matter may need to be removed from the target site by the device and the matter may be various sizes and shapes and positioned at varied locations within the body cavity. The device should allow for extended lengths to be inserted in the body during the operation, such as for cutting of the large masses of matter.
In order to advance the catheter into the body, the guidewire must be fed in a distal direction in order to maintain the position of the guidewire relative to the target site. To address the need to provide extra lengths of catheter and drive shaft, such as during the cutting of long masses, some current devices provide for a limited extra length of catheter, when required, by a sliding member housed within a handheld device. The device must accommodate such sliding of the catheter without disengaging the drive shaft from the drive system. The drive system may need to be slid with the catheter movement. The extension amount is limited by the size of the handheld device and the handheld device may need to be large to accommodate sliding of the catheter. However, a larger handheld device is not usually desirable, especially for a target site that is located far away from the insertion site, because the hand held is placed close to the body and, as a result, there may be a shortage of guidewire length to be pulled as the catheter is advanced.
It is therefore desirable to provide a small, lightweight torque transmission system that allows a driven system to be moved axially relative to a motor drive system where the movement is free of significant friction such that motion is unimpeded and free, even when significant torque loading of the drive system occurs. The connection between the drive shaft and drive system should provide for smooth translation of drive shaft and advancement of the catheter without disengaging from the drive shaft. The system should permit movement with low production of friction. The present invention fulfills these needs and provides further related advantages.